Musnad Ahmad 27:842

'Abd al-Rahman narrated to us, from Malik, from Zayd ibn Aslam, from Ibn 'Umar, who said: Two men came from the East and delivered a speech, and the people were amazed by their eloquence. The Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, some eloquence is magic," or "Indeed, some of eloquence is magic."